It is often necessary to align an optical fiber with another optical fiber, using for instance an optoelectronic device such as a fiber coupler, or a switch. This can involve either carefully aligning the fiber and placing it in contact with the device, or using a lens to allow coupling and alignment over an air gap.
In a laboratory environment, light is coupled into the bare fiber end using a fiber launch system, which uses an objective lens to focus the light down to a fine point. A precision translation stage (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized. However, this arrangement is not suitable for practical use with high power lasers.
Fibers with a connector on the end make the process much simpler: The connector is simply plugged into a pre-aligned fiberoptic collimator, which contains a lens that is either accurately positioned with respect to the fiber, or is adjustable. To achieve the best injection efficiency into the optical fiber, the position and size of the spot and divergence of the beam must all be optimized. With suitable beams, well over 95% coupling efficiency can be achieved.
A problem with devices comprising an adjustable lens is that the accurate positioning required will also require a correspondingly accurate adjustment mechanism. For position control in more than one direction, multiple linear stages may be used together. A “two-axis” or “X-Y” stage can be assembled from two linear stages, one mounted to the platform of the other such that the axis of motion of the second stage is perpendicular to that of the first. A “three-axis” or “X-Y-Z” stage is composed of three linear stages mounted to each other such that the axes of motion of all stages are orthogonal. Some two-axis and three-axis stages are integrated designs rather than being assembled from separate single-axis stages.
An example of a fiber mounting system is shown in U.S. Pat. No. 5,351,330, wherein a lens assembly is supported by a lens holder. The lens holder is positioned by causing deformation to a set of connectors. A problem with this solution is that the deformation is permanent, making re-positioning impossible. Even if a re-positioning would be attempted, any subsequent deformation would weaken the connectors. Also, as the positioning requires deformation of the connectors, rapid or repeatable re-positioning is not possible.
US2003/123808 discloses a similar fiber mounting system in which symmetrical springs are used about a collar in a gimbal system to capture an assembly comprising a ball and an optical or other type of component. Once captured within the mounting system, the ball/component assembly can pivot until an optimal alignment is reached. Once the optimal alignment is reached, the ball/component assembly is fixed using laser welding. A problem with this solution is that the positioning is permanent, making re-positioning impossible.
Depending upon launch conditions and laser power, a misalignment of as little as a few micrometers can cause transmission losses of several hundred Watts in a high-power industrial laser system.
The necessity of having a two- or three-axis adjustment system results in a complicated mechanical design to allow this micrometer precision, however the complexity of the mechanical parts can result in a device that is sensitive to thermal changes or gradients in the system which are commonplace when dealing with high-power industrial lasers.
Hence, there is a need for an improved adjustable device that can be repeatedly re-positioned, rapidly and with high accuracy, but is less complicated and comprises fewer adjustable parts than current solutions.